Manholes provide access to confined spaces or underground structures such as a sewer, boiler, drain or other similar structures. Often, people have to go into such confined spaces, with or without working material. They usually go into and come out of the manhole by means of a long ladder and a protective fence is usually erected around the opening of the manhole in order to prevent people that may pass thereby from falling into the manhole.
People working in manholes occasionally get seriously injured and, as a result thereof, require to be evacuated as quickly and as safely as possible from the manhole in order to be attended by a professional, such as a doctor and the like. The above-mentioned type of manhole-ladder assembly does not enable to quickly, easily, and safely evacuate an injured person from the manhole.
To that effect, tripod hoisting devices have already been developed for attaching a person entering a manhole so that he or she can be recovered in the event of any difficulties. These hoisting devices are also used for lowering and raising the working material necessary for the persons working in confined spaces. These tripod hoists are however cumbersome and once installed over the manhole, they interfere with persons or equipment being passed over the manhole. Examples of these prior art tripod hoists are given in the following US patents: U.S. Pat. No. 4,589,523; U.S. Pat. No. 4,660,679; U.S. Pat. No. 4,824,076.
Also known in the art are the hoisting apparatuses disclosed in U.S. Pat. No. 5,725,070 and U.S. Pat. No. 5,022,489 that are both designed to be secured to a manhole guardrail. These apparatuses are however also cumbersome and, as for the tripod hoists, they extend right over the manhole once installed, thereby interfering with persons or equipment being passed over the manhole. They are thus not very practical for an easy and rapid use.
There is also U.S. Pat. No. 4,838,439 which discloses a hoist apparatus comprising a swivel arm connected to a base member mountable over a manhole. The swivel arm is composed of a vertical post portion and a jib portion. The jib portion is rigidly connected to the post portion and extends upwardly and outwardly therefrom at an angle to the horizontal. A winch is mounted to the post. One drawback with this hoist apparatus is that it is fragile and not suitable for hoisting very heavy persons or objects. It has been shown that the joint connecting the jib portion to the post is not sufficient to resist to the flexion caused by the load hanging at the extremity of the jib portion.
Thus, there is still a need for a hoisting apparatus which would be easily and quickly mountable in the vicinity of a manhole while allowing also to lift very heavy objects or persons without interfering with persons or equipment being passed over the manhole.